1. Field of the Invention
The present invention relates to an image forming apparatus which can prevent an occurrence of a toner image (picture) defect which feigns a white spot or toner scattering by measuring a moisture quantity of a copied print paper to which a toner image is transferred.
2. Description of the Related Art
There is conventionally known an image forming apparatus which employs an electrophotography protocol, such as a copying machine, a printer, a fax machine, or a multifunction device comprising the functions thereof. With the image forming apparatus thus described, a toner image that is formed upon a photosensitive drum by way of an image forming operation is transferred by a transfer device upon a print paper, i.e., a recording paper, whereupon the toner image, which is presently not fixed upon the print paper, is fixed upon the print paper by a fixing device. Thereafter, the print paper whereupon the toner image has been fixed is outputted, i.e., discharged, to a location external to the image forming apparatus.
A moisture quantity, or moisture content quantity (moisture content) of the print paper whereupon the toner image has been transferred, however, varies according to such as a surrounding wherein the image forming apparatus is installed or an internal environment of the apparatus, i.e., such as a temperature or a humidity within the apparatus, and, in order to obtain a high quality image, i.e., a high quality toner image, it is necessary to control an image formation condition, i.e., such as a transfer bias or a fixing temperature, as appropriate to the moisture quantity of the print paper.
The moisture content quantity of the print paper has a particularly significant effect upon the quality of the image, such as, with regard to a transfer portion that transfers the toner image that is formed upon the photosensitive drum upon the print paper, a resistance value of the print paper varies according to a moisture characteristic of the print paper, a change occurs upon the image that is transferred upon the print paper as a consequence of a decline in a toner proportion, i.e., a transfer efficiency, of the transfer by the transfer portion, and a stable, reliable image quality becomes impossible to obtain as a result.
As an instance of the circumstance thus described, a color printer is a key current trend with the image forming apparatus. The color printer creates a rich color image by transferring, in a series of overlays, a plurality of toner images, each toner image comprising a different color. A transfer method known as an interim transfer protocol is known as the transfer method of the color image thus formed. The interim transfer protocol transfer method involves initially performing a multiple overlay transfer, i.e., a primary transfer, of the plurality of toner images, each toner image comprising a different color, upon a transfer body other than the print paper, and thereafter, transferring the color toner image thus formed upon the print paper in a single coordinated transfer, i.e., a secondary transfer.
The interim transfer protocol transfer method is frequently used, owing to the fact that it involves performing the transfer of the color toner image to the print paper in a single coordinated step, thereby conferring an advantage such as requiring few restriction conditions on a layout of the conveyance of the print paper, thus allowing a miniaturization of the apparatus as a whole. Conversely, however, given that the toner image thus formed from the overlay of the plurality of toner images, each toner image comprising a different color, is transferred to the print paper in the single coordinated step by a given transfer bias electric potential value, a risk arises of an image defect occurring, depending upon the moisture characteristic, i.e., the resistance value, of the print paper, such as a toner image, within the toner image thus formed from the overlay of the plurality of toner images, each toner image comprising a different color, that is furthest removed from the print paper, not being transferred to the print paper. It is therefore crucial that the transfer bias electric potential be controlled according to a moisture content state of the print paper.
As a representative instance of such an image defect, consider developing a poor quality image, wherein an image that is painted over a given region, which is referred to as a solid image, is transferred to the print paper such that the toner scatters upon a boundary region of the image. The phenomenon that thus occurs is referred to as a toner scattering or a solid area scattering. In addition, another instance of developing a poor quality image involves the toner, which is assumed to be painted over an entirety of the solid image, as per the preceding circumstance, being not fully transferred to the print paper, giving rise to a break in the image thus transferred, similar to when an insect eats a hole through a leaf. The circumstance thus described is referred to as a white streak or a white spot.
A likelihood of the two types of image defect described herein arising increases when the moisture content quantity of the print paper is low, or, put another way, when the resistance value of the print paper is high, an electric charge that is conferred by the transfer bias electric potential is held upon the print paper, and the image defect thus described occurs as a result of such as either a decline in a transfer efficiency that arises, in turn, from a weakening of an electrical field strength, or an abnormal electrical discharge that arises, in turn, when a voltage that is conferred during a period of high resistance, i.e., when the transfer bias electric potential is extremely large, is itself too strong. Modifying the transfer bias electric potential corrects the situation.
A trade-off exists between the two types of image defect described herein, however, such as is depicted in FIG. 26, wherein controlling the transfer bias electric potential in an attempt to correct for one type of image defect causes the other type of image defect to become more prominent.
In other words, setting the transfer bias electric potential so as to correct for one type of image defect causes the other type of image defect to gradually become more prominent, and the reverse is also true, i.e., setting the transfer bias electric potential to correct for the second type of image defect causes the first type of image defect to gradually become more prominent instead. As a consequence, it is difficult to keep both types of image forming malfunctions under control. A bias electric potential is thus conventionally set to an intermediate portion, wherein neither image defect occurs to a significant degree, as a baseline value. Accordingly, the moisture content state of the print paper is changed, in turn causing a level of the image quality characteristic to decline, such as is depicted in FIG. 27, leading thereby to a state wherein the white spot or the toner scattering occurs.
As a method of controlling and correcting for the image defects described herein, a plurality of image forming apparatuses have been proposed over time, comprising a detection unit that is correlated with the moisture content characteristic of the print paper, wherein the moisture content characteristic of the print paper is specified based on a result of the detection by the detection unit, and a control of the image formation condition is performed in accordance with the moisture content of the print paper.
As an instance thereof, an image forming apparatus that performs the control of the image formation condition in accordance with information that relates to the moisture content of the print paper, and the unit that detects the moisture content of the print paper, is known as per the following:
Japanese Patent Application Laid Open No. 2006-209070 discloses a primary transfer unit that transfers a toner image, which is formed and charged upon a photosensitive body, upon an interim transfer body, a secondary transfer unit, further including a contact transfer body, which sandwiches the print paper against a transfer surface, whereupon the toner image is transferred upon the interim transfer body, and conveys the print paper being further sandwiched between the contact transfer body and the interim transfer body, and an electrode, which is located upon an interior of the interim transfer body, and which impresses a voltage upon the print paper that is sandwiched between the interim transfer body and the contact transfer body, wherein the electrode is employed so as to impress, upon the toner image, by way of a constant current control, a voltage comprising a polarity that is identical to a polarity of the charge that the toner image comprises, and which transfers the toner image from the interim transfer body to the print paper, and a temperature and humidity sensor, which detects an environment surrounding the image forming apparatus, wherein, when the temperature and humidity sensor detects either a low temperature or a low humidity, a correction for a deterioration in an image characteristic is effected thereupon by lowering a size of a transfer current.
Japanese Patent Application Laid Open No. 2005-181701 discloses an image forming apparatus comprising a developing unit that forms the toner image upon an image forming body, and a transfer unit that impresses a bias voltage, thereby transferring the toner image that is formed upon the image forming body to a transfer material, wherein is installed an absolute humidity detection unit that detects an absolute humidity, and, in response to a result of the detection by the absolute humidity detection unit, effects to correct for the deterioration of the image characteristic by shifting the transfer unit in a parallel direction to a direction of a conveyance of the transfer material.
Japanese Patent Application Laid Open No. 2007-304285 discloses using an air duct to remove an atmosphere from a close proximity to an obverse surface of a recording medium while the recording medium is in transit upon a conveyance path, positioning a sensor unit portion upon an atmospheric exhaust port, whereupon the atmosphere thus removed is directed, and positioning a thermal conductivity protocol humidity sensor, which is formed by employing an MEMS technology, upon the atmospheric exhaust port, wherein a humidity of the atmosphere thus directed is detected, and a control unit estimates a moisture content quantity of an obverse surface layer of the recording medium in accordance with an output of the humidity sensor, and sets an image forming process control condition according to the moisture content quantity thus estimated.
Japanese Patent Application Laid Open No. 2007-322558 discloses a moisture content quantity estimation device, including a first detection unit that detects a first information relating to a moisture content quantity of a sheet material, either making contact with the sheet material, or in a location close to the sheet material, and further including the steps of detecting the first information relating to the moisture content of the sheet material, detecting a second information relating to a factor that affects the information relating to the moisture content of the sheet material, calculating a predictive estimate of a moisture content quantity of the sheet material in accordance with the first information and the second information, and adjusting an image forming process control condition in accordance with the moisture content quantity estimate thus computed, wherein a thermal conductivity protocol humidity sensor, which is formed by an MEMS technology, is employed as the first detection unit.
Japanese Patent Application Laid Open No. H9-204080 discloses a configuration wherein a heat roller is installed upon a fixing portion of an image forming apparatus, whereupon a thermal fixing control is performed, as well as upon a portion of a print paper conveyance portion where upon the print paper traverses, wherein the heat roller is employed to heat the print paper, a water vapor that arises as a result of the heat thus imparted to the print paper is detected by a humidity sensor, and an achievement of a positive image quality characteristic is effected by changing a control condition of each respective process of an image formation, i.e., transfer and fixing, in accordance with information that is detected by the humidity sensor.
Japanese Patent No. 3,486,589 discloses a configuration including a charging unit that charges, by way of an image forming unit that electrostatically forms the toner image upon a transfer material, a surface of the transfer material whereupon the toner image is formed, prior to the toner image being formed upon the transfer material, so as to be charged with a polarity that is opposite to a regular charge polarity of the toner, a control unit that controls a voltage that is impressed upon the charging unit in accordance with a length in a direction that is effectively orthogonal to the direction of the conveyance of the transfer material, and a humidity detection unit, wherein an achievement of a high quality color image characteristic is effected by the voltage that is impressed upon the charging unit being controlled by the control unit, in accordance with a result of a detection by the humidity detection unit.
Japanese Patent Application Laid Open No. 2006-242710 discloses a configuration including a moisture content quantity detection sensor and a control unit, wherein a CPU of the control unit determines a temperature by consulting a temperature table, in accordance with a frequency data that is acquired from the moisture content quantity detection sensor in a state wherein the print paper is not present within an electrostatic capacity region of the conveyance path, determines a moisture content quantity that is contained within the print paper by consulting a moisture content quantity table, in accordance with the frequency data that is acquired from the moisture content quantity detection sensor in the state wherein the print paper is not present within the electrostatic capacity region of the conveyance path, a frequency data that is acquired from the moisture content quantity detection sensor in a state wherein the print paper is present within the electrostatic capacity region of the conveyance path, and the temperature that has been previously determined, and provides a feedback of a degree or quantity of control for a control of an image formation in accordance with a result of the determination thus performed.
Japanese Patent Application Laid Open No. 2004-54163 discloses a configuration wherein an obverse surface of the print paper, i.e., the transfer material, is brought into contact with a pair of conductive rollers, whereupon a voltage has been impressed, a specific resistance of the obverse surface of the print paper is detected, the specific resistance of the obverse surface of the print paper thus detected is converted into the moisture content quantity of the print paper, and an achievement of a correction of an image quality characteristic is effected by applying a moisture to the print paper, when the moisture content quantity of the print paper is less than a standard value.
Japanese Patent Application Laid Open No. 2004-216883 discloses a configuration including a conductive material, as a detection unit, wherein a specific electrical resistance of the conductive material varies according to a moisture content quantity of a print paper, either when the print paper traverses the conductive material or the print paper comes into contact with the conductive material, a value that is detected by way of the change in the specific electrical resistance resulting there from is compared with an information that is stored within a memory portion that is installed into the apparatus, and an ambient humidity computed thereupon, wherein an external force is applied to the print paper, a characteristic of the print paper, such as a thickness or a hardness of the print paper, is simultaneously acquired thereby, and an image formation condition with respect to the print paper to be printed upon is controlled in accordance with the information thus acquired.
Japanese Patent Application Laid Open No. H7-234556 discloses a configuration including a control unit, which projects a light upon the print paper, derives a proportion of moisture content of the print paper according to a change in a wavelength of the light that is reflected from the print paper, and corrects each respective image formation condition thereby.
Japanese Patent Application Laid Open No. 2005-249889 discloses a configuration wherein a unit is installed that derives a moisture content quantity from a resistance value that arises when the voltage is impressed upon both surfaces of a transfer material, varies a condition of contact between the transfer material and the image forming body, as well as the transfer bias electric potential, according to the moisture content quantity thus derived, and maintains a favorable severance characteristic for separating the transfer material from the image forming body.
In addition, a detailed research paper regarding a water vapor distribution is also known; refer to the cited non-patent references 1 and 2 hereinafter for details.
The cited non-patent reference 1 depicts an existence of a region, known as a diffusion layer, wherein, when the moisture content evaporates, a movement of the moisture content, i.e., the water vapor, is performed in a linear fashion from a location whereat the evaporation of the moisture content commences.
In addition, the cited non-patent reference 2 denotes that a steady movement of the water vapor in a constant quantity is possible for water, when the water is at a surface level, as an instance thereof, and it is possible for a thickness of the diffusion layer, when not affected by such as a wind acting thereupon, to be present within a region ranging from surface level to a height on the order of 10 mm in a perpendicular direction, and for the thickness of the diffusion layer to comprise a height of 2 mm to 3 mm or thereabouts without difficulty even if the wind does exert an effect thereupon.
With the print paper, however, the moisture content quantity that is contained by the print paper varies depending on an ambient environment whereupon the print paper is present. Thus, the water vapor movement thereupon is not steady, nor is the quantity of the water vapor constant, such that, when dealing with a very small quantity of moisture, the region of the thickness of the diffusion layer becomes smaller still, and it is necessary to detect the water vapor that is arising from the print paper at an infinitely close distance from the obverse surface of the print paper, in order to accurately detect the water vapor thus arising therefrom.
Cited Non-Patent Reference 1:    Ueda, Masabumi: “Measurements of the Gradient of Water-vapour Pressure and the Diffusion Coefficient,” Jpn. J. Appl. Phys. (OYO BUTURI), Vol. 25, No. 4(1956), p. 145, The Japan Society of Applied Physics (OYO BUTURI GAKKAI)
Cited Non-Patent Reference 2:    Ueda, Masabumi: “Rate of Evaporation of Water by Forced Convection,” Jpn. J. Appl. Phys. (OYO BUTURI), Vol. 29, No. 7(1960), p. 443, The Japan Society of Applied Physics (OYO BUTURI GAKKAI) 1960.
Whereas the disclosure according to Japanese Patent Application Laid Open No. 2006-209070 shows a configuration whereby the temperature and humidity sensor detects the environmental humidity whereupon either the transfer device or the image forming apparatus is installed, and controls the electrical current value of the electrode that is installed upon the transfer portion, it is the moisture characteristic of the print paper that is significantly related to the image quality characteristic, and thus, a degree of irrationality arises in detecting the environmental temperature and humidity wherein the apparatus or the device is located, and treating the temperature and humidity thus detected as the moisture characteristic of the print paper.
As an instance thereof, when the environment wherein the apparatus or the device is located is a high humidity environment, and the print paper is left in the environment thus constituted for an extended period of time, the print paper will eventually contain a significant amount of moisture. If the apparatus or the device is operated in such a state, the environment wherein the apparatus or the device is located will be in a state that is similar to the state of the print paper, and thus, the printing operation will be performed without impairing the image quality characteristic.
If the humidity in the ambient environment should be dramatically lowered, however, owing to such as air conditioning, the moisture that is contained within the print paper will not rapidly evaporate. As a consequence, the print paper will remain in the state of containing the significant amount of moisture for an indeterminate period of time. The print paper that is stacked upon such as a cartridge for loading the print paper upon the apparatus or the device will be particularly slow to adapt to a change in the environment, and the state of the print paper thus stacked will be clearly inappropriate as a result.
If the printing operation is performed in such a state, the environment of the apparatus or the device will have changed to a low humidity environment, and thus, the apparatus or the device will perform the control of the image formation in accordance with the low humidity environmental condition setting. The print paper that is actually conveyed upon the apparatus or the device, however, is still in the high humidity state, thus giving rise to the image formation defect or a defect in the conveyance of the print paper.
If only one sheet of print paper is contained within the print paper cartridge, a significant proportion of the obverse surface of the print paper will come into contact with the ambient environment, such that the print paper will more easily adapt to the ambient environment, and the print paper will accordingly dry out more rapidly. If dozens of sheets of the print paper are stacked within the print paper cartridge within the image forming apparatus, however, a smaller proportion of the obverse surface of each respective sheet of the material of the print paper will instead come into contact with the ambient environment, such that each respective sheet of the material of the print paper will dry out much less readily as a result.
Accordingly, when it is determined that the state of the moisture content of each respective sheet of the print paper is identical to the environment wherein the apparatus or the device is located, and the determination thereof is taken into account in the electrical current value control information, the actual state of the moisture content actually differs from the state thus determined, and it will be apparent therefrom that a malformation will arise with the image formation thereupon.
Whereas the disclosure according to Japanese Patent Application Laid Open No. 2005-181701 shifts the transfer unit, treating the result that is detected by the absolute humidity detection unit as the moisture characteristic of the transfer material, i.e., the print paper, the transfer material, i.e., the print paper, has a moisture characteristic that is dependent upon a relative humidity, and thus, as an instance thereof, if a print paper with the same moisture characteristic is detected with a different environmental temperature, the value of the relative humidity will vary, as will the trend of the variance of the value of the relative humidity.
As a consequence, even if the result of the detection by the absolute humidity detection unit is employed to control the transfer unit, the value of the relative humidity varies according to the temperature, interfering with the control being made that is appropriate to the ambient humidity, and thus preventing obtaining a desirable image.
Whereas the disclosure according to Japanese Patent Application Laid Open No. 2007-304285 has a configuration wherein the atmosphere that is removed from the obverse surface of the sheet of the material of the print paper by the air duct is directed, and the humidity of the atmosphere thus directed is detected, it is believed that the atmosphere that is removed from the obverse surface of the sheet of the material of the print paper by the air duct will be directed efficiently only when a sheet of the material of the print paper is conveyed that maintains a higher state of moisture content than the humidity of the environment wherein the units are installed.
When the sheet of the material of the print paper either discharges or adsorbs moisture according to an equilibrium between the sheet of the material of the print paper and the ambient environment, and the sheet of the material of the print paper is conveyed that comprises a lower moisture content state than the ambient environment, the atmosphere will not flow within the duct. In addition, even if the atmosphere within the duct should be adsorbed within the sheet of the material of the print paper, a shape of an aperture portion of the duct will comprise a shape that impedes a reverse flow of the atmosphere with respect to the sheet of the material of the print paper. It is thus believed that the sheet of the material of the print paper that is being conveyed will traverse the air duct before the atmosphere may be directed to the sheet of the material of the print paper that is being conveyed, and it is further believed that a problem such as a delay in the detection of the humidity of the atmosphere thus directed will result from the phenomena described herein, giving rise to a malfunction wherein it will be possible to detect only the moisture state of the print paper that comprises a specified moisture characteristic.
The disclosure according to Japanese Patent Application Laid Open No. 2007-322558 comprises a configuration wherein the moisture content of the sheet of the material of the print paper, whereupon the image process operation is performed, is estimated in accordance with the value that is detected by the first detection unit, which detects, in the location that is in close proximity to the sheet of the material of the print paper, the humidity thereof, and the information that is detected by a second detection unit, which is installed within a periphery of the conveyance path within the apparatus. In other words, the second detection unit measures the environment of the periphery of the conveyance path, or, put another way, the environment within the apparatus, and estimates the moisture content quantity of the print paper, which is believed to vary according to the effect of the environment being thus measured.
A distribution of the temperature and humidity is inevitably present, however, within the ambient temperature and humidity of the environment within the apparatus or the periphery of the conveyance path. As an instance thereof, installing the detection unit upon the periphery of the conveyance path, within a proximity to the fixing device, which is configured to perform the thermal fixing, resulting in a comparatively high temperature environment. Conversely, installing the detection unit upon the periphery of the conveyance path, close to a print paper supply portion whereupon is stored the sheet of the material of the print paper, results in a comparatively low temperature environment. Furthermore, it is believed that the environment of the transfer portion that transfers the toner material to the sheet of the material of the print paper will vary from the environment of the other locations described herein. In addition, even when an ongoing series of printing operations is performed, the environment of each respective image formation process portion changes with each successive print in the series, according to a quantity of the prints that is performed in the series and the time required for the print series.
The estimated value of the moisture content of the sheet of the material of the print paper thus varies significantly depending upon the location whereupon the detection unit is installed. Thus, performing the control of each respective image process according to the moisture content value thus estimated cannot be considered to be desirable, and it would be necessary to install a third, fourth, and fifth detection unit for each respective image process, i.e., such as developing, transfer, and fixing, in order to employ the method described herein to solve the problems described herein. Presuming such a configuration, however, causes an increase in a quantity of components, and inevitably raises costs, making the configuration described herein unsuitable for practical application.
In addition, even presuming a configuration wherein the first detection unit is moved around and performs the task of both the first and the second detection units, it is possible, depending on a distance to be traveled by the first detection unit, that no noticeable difference may be found in the detected value in the proximity to the sheet of the material of the print paper and the detected value elsewhere within the apparatus. Avoiding such a problem by extending the distance to be traveled will require increasing a time required for such a travel, resulting in a malfunction wherein it would not be possible to support a high speed printing environment (to be described hereinafter). In addition, it would be possible that the environment prior to the movement of the detection unit would itself be moved around to the location of the environment subsequent to the movement of the detection unit, by the movement of the detection unit thereupon.
In addition, anticipating a disruption of the detected value by a flow of the atmosphere that arises when the detection unit is moved, and attempting to move the detection unit slowly in order to prevent such a problem from occurring, gives rise to a malfunction with a image forming apparatus manufactured in recent years whereupon the high speed printing is being advanced, wherein the detection fails to keep pace with the speed of the conveyance of the print paper.
The problems thus described become more prominent the higher the sensitivity and responsiveness of the sensor become, such as with the thermal conductivity protocol humidity sensor, which is formed by employing the MEMS technology, and thus, it is believed that the technologies described herein would not be suitable for practical application.
When the print paper is heated as per the disclosure according to Japanese Patent Application Laid Open No. H9-204080, the water vapor content that arises therefrom varies according to the moisture content quantity that is contained by the print paper. As an instance thereof, a large quantity of the water vapor is generated when the print paper that comprises a significant moisture content is heated. When the water vapor arises particularly with respect to such as the fixing portion, which performs the thermal fixing process, it is anticipated that the water vapor condenses into droplets that adhere upon the periphery of the apparatus, resulting in a dew formation state thereupon.
A risk exists that the droplets that have adhered within the apparatus may remain thereupon, causing the image defect, the defect in the conveyance, or moreover, a defect in the apparatus proper. Such as an exhaust feature is thus necessary to specifically remove the droplets therefrom. In addition, the print paper comprises the moisture content or moisture content proportion that is optimal when forming the image, i.e., 4% to 6% or thereabouts, and thus, when heat controlling the print paper during the conveyance prior to forming the image, the moisture content proportion varies thereupon, such that a risk exists that the moisture content proportion of the print paper may decline, in turn causing a deterioration in the image quality thereby.
Whereas the disclosure according to Japanese Patent Application Laid Open No. H9-204080 includes performing the partial heating of the print paper and ascertaining the quantity of the water vapor that arises as a result, the quantity of the water vapor that arises thereby will be minute when the moisture content quantity that is contained by the print paper is itself very small. In such a circumstance, the water vapor that arises thereby will easily adapt to the ambient environment, making it impossible to identify a difference between the water vapor and the ambient environmental conditions, in turn complicating the accurate control of the print paper thereupon.
The disclosure according to Japanese Patent No. 3,486,589 comprises the temperature and humidity sensor being positioned upon an upper portion of the print paper cartridge, wherein the print paper is stacked for storage, with the temperature and humidity sensor computing the moisture content quantity of the print paper from the absolute moisture quantity that is detected thereby upon a periphery of the upper portion of the print paper cartridge. The ambient environment of the loading cartridge whereupon the print paper is stacked is measured therewith. As an instance thereof, if the moisture content state varies between the print paper that comprises the upper portion of the stack, the print paper that comprises a middle portion of the stack, and the print paper that comprises a lower portion of the stack, a circumstance of a state wherein the various moisture content states are mixed and offset one another will be detected as a result, allowing the control condition to be determined according to the ambient environment whereupon a bundle of the print paper and the apparatus are located, without regard for the moisture content quantity of a single sheet of the print paper. Thus, the image formation defect of the defect in the conveyance thereof may arise, owing to the fact that the control condition will not match if the print paper with the moisture characteristic that differs from the moisture characteristic that was detected by the process described herein is used in the image formation instead.
The disclosure according to Japanese Patent Application Laid Open No. 2006-242710 includes placing a coil portion, in a state wherein a high frequency voltage is impressed thereupon, of the moisture content quantity detection sensor in opposition to a metallic or other conductor, giving rise to an electrostatic conjunction between the coil portion of the moisture content quantity detection sensor and the conductor, wherein the frequency of the high frequency voltage that is impressed upon the coil portion fluctuates according to the distance between the coil portion and the conductor. In order to employ the principle thus depicted, the moisture content quantity detection sensor is positioned so as to sandwich the conveyance path whereupon the print paper is conveyed, as well as in opposition to, and at a given distance from, the coil portion and a metallic print paper conveyance guide, such that, when the print paper traverses the electrostatic capacity region that is formed between the coil portion of the moisture content quantity detection sensor and the print paper conveyance guide that is in opposition to the coil portion of the moisture content quantity detection sensor, a dielectric constant of the electrostatic capacity region increases as a result of the print paper traversing therethrough, thereby causing an oscillation frequency of an oscillator circuit of the moisture content quantity detection sensor to change. The moisture content quantity of the print paper is thus determined in accordance with a quantity of the variation of the oscillation frequency thus detected. It is inevitably necessary, however, for the metallic conductor to be located in opposition to the coil portion in such a circumstance. Consequently, the print paper conveyance guide must also inevitably be metallic in nature, and, in addition to becoming a constraining condition for a design of the apparatus, it is necessary for the coil portion and the conductor portion to be installed as close to parallel to one another as possible. A risk is present that an accurate detection of the value of the moisture content may not be possible if the coil portion and the conductor portion differ from the parallel by so much as less than one degree, demanding a high degree of precision in component assembly during the process of the manufacture of the image forming apparatus, which in turn increases such as a number of the manufacturing processes thereupon, none of which is desirable in terms of price-performance.
In addition, the result of the detection varies according to the ambient temperature, and thus, while the determination of the moisture content is performed according to a data of the moisture content quantity table, the detection varies according to distance, and the accurate detection thereof would become impossible if a location for the installation of the moisture content quantity detection sensor or the conveyance guide should be distorted, thereby changing the distance therebetween. Furthermore, if such materials as dust, arising from such as bits of paper, or droplets formed by condensation, adhere to the conveyance guide, the electrostatic capacity will be altered, leading to a decline in a reliability of the detection of the moisture content quantity thereupon.
Whereas the disclosure according to Japanese Patent Application Laid Open No. 2004-54163 comprises a basic configuration of the steps of impressing the voltage upon the obverse surface of the print paper, measuring the resistance value between one or more terminals subsequent to the impression of the voltage, and converting the result of the measurement into the moisture content of the print paper, in order to derive the resistance value of the obverse surface and the reverse surface of the print paper and convert the resistance values thus derived into the moisture content of the print paper, it is not possible to perform a stable measurement if the voltage that is impressed upon the print paper is a low voltage. Thus, a high voltage on the order of hundreds of volts is impressed upon the print paper, necessitating a charging time in order to obtain the high voltage required. A malfunction thus occurs in that, when a plurality of sheets of the print paper is conveyed at high speed, such as when performing a series of print jobs all at once, the measurement of the resistance value of the print paper will not keep up with the speed at which the print paper is being conveyed.
In addition, the resistance value of the print paper is unstable immediately subsequent to the impression of the voltage upon the print paper, and thus, it would be desirable to measure the resistance value of the print paper on the order of one minute subsequent to the impression of the voltage upon the print paper. A certain amount of time would also be necessary in order to accurately measure the resistance value of the print paper, and thus, a malfunction arises wherein the measurement of the resistance value of the print paper will not keep up with a series of print jobs being performed all at once. Furthermore, the specific resistance of the print paper varies according to the effect of the ambient temperature and the ambient humidity of the environment whereupon the measurement is performed, and thus, a risk is present of not being able to detect the moisture content quantity of the print paper in an accurate and stable manner.
In addition, recent types of print paper that are employed with the image forming apparatus have either been coated with a chemical upon the obverse surface thereof, or had a special obverse surface process performed thereupon, in order to increase the quality of the image that is formed thereupon. When bringing the print paper that has thus been treated into contact with the pair of conductive rollers whereupon the voltage has been impressed, and detecting the specific resistance of the obverse surface of the print paper, it is difficult to accurately detect the specific resistance of the obverse surface of the print paper under conventional circumstances, thus precluding the accurate detection of the moisture content quantity of the print paper. Moreover, an error in the detection of a change in the resistance runs a risk of erroneously conferring the moisture upon such as the specially treated paper, thereby restricting the print paper that is employed upon the image forming apparatus.
In addition, acquiring the information of the characteristic of the print paper requires a transformation portion that transforms the value that is detected by the detection portion into the characteristic of the print paper, a memory portion for storing the information of the print paper that is to be used for distinguishing the type of the print paper, and a discrimination portion that compares the information that is stored in the memory portion. Accordingly, a configuration aside from the detection portion will be required, further complicating the configuration of the apparatus.
A configuration that applies the external force in order to obtain the information of the thickness or the hardness of the print paper is also complicated, and will require a dedicated space in order to be installed within the image forming apparatus.
When leaving a plurality of sheets of print paper that comprise the same moisture content respectively in environments of different temperature and humidity, the quantity of variation of the ambient humidity in close proximity to the print paper differs therebetween, and a malfunction arises wherein the moisture content quantity that is contained within the print paper cannot be determined solely by detecting the ambient temperature and humidity.
While the configuration described herein acquires the data by comparing the value that is detected by the detection portion with the data that is stored upon the memory portion, even when considering only a single type of the print paper, storing all of the relationships between the moisture content quantity and the temperature and humidity would require a tremendous amount of data capacity, and a problem occurs in that a consideration of the cost-benefit ratio leads to a conclusion that the configuration described herein is lacking in practical application.
Even if the print paper comprises the same moisture content quantity, in a state wherein the configuration comes into contact with the atmosphere that is in close proximity to the print paper and the print paper, the effect of the temperature and humidity of the space wherein the atmosphere that is in close proximity to the print paper and the print paper differs, and thus, a risk is present that the information of the detection of the moisture content of the material of the sheet of printing paper will change.
It is conceivable that it would not be possible to distinguish the characteristic of the print paper without applying an impact to the print paper by way of the external force thereupon, as well as that a fiber composition of the obverse surface of the print paper will be altered by the application of the external force thereto, thereby running a risk of a problem occurring with the image quality.
The disclosure according to Japanese Patent Application Laid Open No. H7-234556 presumes a configuration comprising, at an absolute minimum, a signal processing portion that controls an optical signal, a light emission portion that emits the optical signal, a light reception portion that receives the optical signal, and a calculation processing portion that determines the moisture content of the print paper from the optical signal thus received, wherein the light emission portion and the light reception portion must be respectively installed upon a site whereupon the print paper traverses, and in a location wherein the light emission portion and the light reception portion sandwich the print paper, in opposition to one another. In the present circumstance wherein the demand is for miniaturization and cost reduction of the image forming apparatus, the configuration as described herein leads to an increase in the number of components and thus an increased cost, as well as requiring creating two spaces in order to install the light emission portion and the light reception portion in the location such that the light emission portion and the light reception portion sandwich the print paper, in opposition to one another, which may result in a factor that interferes with the miniaturization of the image forming apparatus.
In addition, a risk occurs wherein the detection operation may become unstable, owing to a possibility that an unforeseen refraction or reflection of the light may occur as a result of a change in the ambient environment, i.e., the temperature, the humidity, or the wind, or such as a change in the distance or the region of the detection, arising from the droplet or the bits of paper adhering to either the light emission portion or the light reception portion.
Furthermore, a risk arises wherein, if such as the droplet adheres to the light emission element or the light reception element, by way of such as the condensation thereupon, it will not be possible to emit or receive the light in the normal state, and thus, it will not be possible to make an accurate detection thereby. In addition, the light emission intensity of an LED light source that is frequently used as the light emission element is characterized by weakening in an inverse proportion to a total light emission time. As the light emission intensity weakens over time, the light that is reflected from a material to be measured becomes fainter, an output from the light reception element becomes unstable, and a precision of the detection thereby deteriorates as a result.
The disclosure according to Japanese Patent Application Laid Open No. 2005-249889 comprises a configuration wherein the print paper moisture content detection unit further comprises a configuration that is approximately identical to the configuration disclosed according to Japanese Patent Application Laid Open No. 2004-216883, and a width of a nip of the transfer portion and the transfer bias electric potential is controlled according to the result of the detection of the moisture content of the print paper. A malfunction arises, however, wherein the accurate control of the transfer portion in accordance with the state of the moisture content of the print paper is complicated as a result.
Moreover, when the plurality of the print paper traverses the print paper conveyance path in a series, such as in a circumstance wherein the print paper is supplied and printed in a series, i.e., an image formation in a series, the environment within the image forming apparatus varies according to the moisture content quantity of the print paper. As an instance thereof, when printing in series upon a series of sheets of print paper with a high moisture content, the interior of the image forming apparatus will be changed into a state of high humidity. As a result, the condensation may occur upon the fixing device, which thermally fixes the image upon the print paper, or a filming phenomenon may occur upon such as the developing device, wherein a discharge generation material, which adheres to the obverse surface of the photosensitive drum, adsorbs the moisture content, which may in turn cause the image quality defect.